Bacteria are characterized by having no nucleus or any inner structures defined by membranes. The chromossomes are free, organized in a cyclic pattern inside the cell.

Bacteria are formidable decompositors and pathogenics, but some have other fucntions. Rhizobium bacteria, associated with the roots of Leguminosae (e.g. peas, beans, soy) are responsible for Nytrogen fixation to the soil, making this valuable element available for the plants.

Other group of bacteria incidentally inject part of their DNA into the roots of some plants, whose cells assimilate this DNA to its own. The plants become naturally "transgenic". Based on this process, biotechnology labs are developing artificially transgenic plants by selecting certain genes, in order to make them pest-free, dry-tolerating, faster growing, or just tougher than the original species.